Twin pull down chain equalizer

ABSTRACT

An equalizer assembly for maintaining tension in the chains used to drive a drill stem rotating mechanism of a blast hole drill has two spaced, floating equalizer frames, each of which includes a pair of chain engageable sprockets. An equalizer bar connected between the frames is pivotally attached at its midpoint to a slide member actuated for vertical displacement by a hydraulic cylinder, this arrangement enabling the equalizer frames to shift in response to variable chain pressures in order to keep the chains taut with equal tension.

United States Patent [191 Nelmark et al.

[ Dec. 17, 1974 TWIN PULL DOWN CHAIN EQUALIZER [75] Inventors: Jack D. Nelmark, New Berlin;

Matthew Smith, Milwaukee, both of Wis.

[73] Assignee: Bucyrus-Erie Company, South Milwaukee, Wis.

[22] Filed: Nov. 26, 1973 21 Appl. No.: 419,218

[52] US. Cl. 173/140, 74/2429, 74/242.11 C, 173/147 [51] Int. Cl E2lb 7/02 [58] Field of Search 173/26, 140, 147; 74/242.11 C, 242.1 FP, 242.9

[56] References Cited UNITED STATES PATENTS 11/1946 Brown 173/44 6/1958 Colquilt 2,869,826 1/1959 Thornberg 173/23 2,972,388 2/1961 Thornberg 173/23 3,198,263 8/1965 Reischl 173/26 3,474,872 10/1969 Danuser 173/140 Primary ExaminerJames A. Leppink Attorney, Agent, or FirmQuarles & Brady 57 ABSTRACT An equalizer assembly for maintaining tension in the chains used to drive a drill stem rotating mechanism of a blast hole drill has two spaced, floating equalizer frames, each of which includes a pair of chain engageable sprockets. An equalizer bar connected between the frames is pivotally attached at its midpoint to a slide member actuated for vertical displacement by a hydraulic cylinder, this arrangement enabling the equalizer frames to shift in response to variable chain pressures in order to keep the chains taut with equal tension.

3 Claims, 10 Drawing Figures BACKGROUND OF THE INVENTION The invention relates to an equalizer device for the pull down and hoisting chains of a drill string rotating mechanism and more particularly to an automatic, hydraulically actuated equalizer device having frames which float within the structure of a mast of a drilling rig. The preferred embodiment is especially useful in the tensioning of chains in a rotary blast hole drill, but the invention is not limited exclusively to this application and may be utilized wherever it is desirable to minimize slack in the driving chains of drill string rotating apparatus.

Typical rotary drilling machines employ endless roller chains to interconnect a rotary drill string head with a drive system in order to effect longitudinal pull down and hoisting of the drill string head relative to the mast of the machine. Such chains are typically arranged in closed loop formation and are utilized in pairs, each being symmetrically positioned about the longitudinal axis of the drill string. In the operation of these drilling machines, total downward forces in the range of 20,000 lbs., or 10,000 lbs. of transmitted force per chain, are often applied at the upper end of the drill string. It becomes necessary, therefore, to constantly maintain the dual roller chains in a taut condition in order to eliminate straining of the mast and to apply an equal balance of forces for effective drilling.

A device for equalizing the tensions in pull down and hoisting chains is disclosed in U.S. Pat. No. 3,l98,263 issued to K. E. Reischl on Aug. 3, I965. The roller chains of the drill string mechanism in that patent engage a pair of spring biased sprockets on each of two channel members which may be shifted vertically by means of an equalizer bar-bell crank arrangement. All the chain tightening force exerted during pull down and hoisting operations is derived solely from the biasing springs of the sprockets, and the channel members often require frequent, supplementary manual adjustment in order to insure equal loading of the roller chains. The present invention is intended to improve upon the Reischl construction.

It is extremely important to limit the amount of slack which normally appears during the chain pull down and hoisting operations. Roller chains typically have a tolerance factor of one-sixty-fourth of an inch per foot of chain, and when used in closed loop lengths of 140 feet or more, a looseness in excess of 2 inches may occur. If proper, equal tensioning of the chains cannot be maintained there is a resultant imbalance in drilling force at the rotary head which significantly impairs the efficient penetration ofthe strata being drilled. in addition, stabilization of the mast is affected by adverse twisting pressures. Tightening of the chains must also be provided during setup and takedown of the drill mast such that the chains will not become disengaged from the sprockets of the drilling apparatus. Heretofore, it has been necessary to apply frequent, manual adjustment of equalizer arrangements in attempting to provide continual tensioning for the chains. Such adjustments, however, have proven to be very difficult and result in extraneous costs due to the necessity for increased manpower and down time expenditures.

It is against this background of deficiencies that the present invention has been conceived, and a principle purpose of the invention to improve upon prior chain equalizing devices which furnish variable, nonautomatic tensioning of drive chains.

SUMMARY OF THE INVENTION The present invention provides an equalizer arrangement for the dual pull down and hoisting chains of a rotary drilling machine having two spaced, chain engageable equalizer frames, an equalizer bar connected between the frames, a slide member pivotably attached to the equalizer bar and a hydraulic cylinder affixed to the slide member.

In the preferred form of the invention, rotatable sprockets included on each of the equalizer frames, are in peripheral contact with a closed loop chain intermediate to the drill string rotary head and the drive system. The hydraulic cylinder is actuated to vertically displace the slide member which in turn pivots the equalizer bar causing the equalizer frames and engageable chains to shift in response to variable pressures and maintain a continual, simultaneous automatic tensioning of the chains.

It is a general objective of the invention to provide a chain equalizer which automatically reduces slack from the twin pull down and hoisting chains of rotary drilling apparatus by utilization of a constant acting hydraulic cylinder. This feature eliminates the structural need of dual spring biased chain sprockets on each of the frame or channel members which were previously employed to produce tension on the chains during all modes of drilling. The biasing sprocket of this invention is not relied upon for tightening during pull down and hoisting but serves only to reduce slack during mast positioning at which time the hydraulic cylinder is relaxed.

Another objective is to enable a better.controlled tensioning assembly in which the equalizer frames are allowed to float within the confines of the mast rather than be pivotally affixed to the mast. This allows for a more positive, reliable driving force to be transmitted to the rotary head. I

A further object is the provision of a simple and economical one piece, centrally pivoted equalizer bar whose end portions are fixedly joined to the equalizer frames enabling a more direct balancing of forces in contrast to the pivotal link arrangement disclosed in the aforementioned US. Pat. No. 3,198,263.

The foregoing and other objects and advantages of the invention will appear from the following description. In the description reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration and not of limitation a preferred embodiment of the invention. Such embodiment does not represent the full scope of the invention, but rather the invention may be employed in many different embodiments, and reference is made to the claims herein for interpreting the breadth of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary, side view in elevation of the chain pull down and hoist structure of a rotary blast hole drill incorporating a chain equalizer of the present invention,

FIG. 2 is an enlarged front view in elevation of the chain equalizer taken in the plane 2-2. designated in FIG. 1,

FIG. 3 is a view in cross section of a hydraulic cylinder, slide member and equalizer bar taken in the plane 33 designated in FIG. 2,

FIG. 4 is a view in cross section of the slide member of FIGS. 2 and 3 taken in the plane 4-4 designated in FIG. 2,

FIG. 5 is a view in cross section of an equalizer frame and carrier insert taken in the plane 5-5 designated in FIG. 2,

FIG. 6 is a view in cross section of an equalizer bar end taken in the plane 66 designated in FIG. 5,

FIG. 7 is a fragmentary view in cross section of the upper end of an equalizer frame taken in the plane 7-7 designated in FIG. 2,

FIG. 8 is an enlarged view in cross section of the equalizer frame and carrier insert taken in the plane 88 designated in FIG. 5,

FIG. 9 is a view in cross section of the equalizer frame and carrier insert taken in the plane 9-9 designated in FIG. 5, and

FIG. 10 is a view in cross section of the carrier insert taken in the plane ll0 designated in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown a pull down and hoist mechanism for the drill string of a rotary blast hole drill. A mast l is pivotably adjustable about a shaft 2 by means ofa hydraulic ram 3 between a horizontal storage position and a series of variable, raised drilling positions, such as the vertical attitude illustrated. A conventional drill string rotating mechanism 4 including a pair of pinions 5 in mesh with racks 6 fixed on the mast 2 and a pair ofrotary drive sprockets 7 is raised, or lowered longitudinally along the mast 2 by the use of a pair of endless roller chains 8. Each of the chains 8 forms a closed loop interconnecting the drill string rotating mechanism 4, with a driving sprocket 9 that is mounted on the shaft 2 and driven by a main drive system 10 of a type as disclosed in said US. Pat. No. 3,198,263. Each of the formed loops of chain 8 passes around an idler sprocket at the top of the mast 2 and extends through a chain equalizer, generally identified by the numeral 11, which is located near the bottom of the mast 2. By powering the main drive system 10 a pull down or hoisting force is transmitted through the drive sprocket 9 and the chains 8 to the drill string rotating mechanism 4. The chain equalizer 11 serves to constantly maintain equal tension in each of the loops of chain 8, and the present invention resides in the construction of this equalizer II. It should be appreciated that while the invention is particularly suitable for rotary blast hole drills, it is also applicable to any other drilling equipment wherein equalized tensioning of twin pull down and hoisting chains is required.

Referring to FIGS. 2-4, the mast 2 includes a pair of uprights interconnected by crossbracing that comprises a transverse. hollow beam 12 and a cylindrical crosstube 13. Extending vertically through the longitudinal center of the transverse beam 12 is a rectangular guide way 14 defined by a front wall 15 of the beam 12, a pair of laterally spaced guide plates 16 extending above the top of the beam 12, and a rear wall 17. An inverted. U- shaped frame 18 is secured to and rises above the laterally spaced guide plates 16, and hung inside the frame 18 is a hydraulic cylinder 19. The bottom, or rod end 20 of the cylinder 19 is pin connected to the upper end 21 of a slide member 22 that extends through the guideway 14 for vertical, reciprocating motion in response to actuation of the cylinder 19.

The slide member 22 is built up of three plates sandwiched together. An inner plate 23 is narrower and shorter than a pair of like, outer plates 24, so that the upper end 2] and the lower end 25 of the slide member 22 are bifurcated as shown in FIG. 3. The lower, bifurcated end 25 of the slide member 22 extends below the bottom of the cross beam 12 and is pivotal to the longitudinal center of an equalizer bar 26 by means of a pivot pin 27, which pin 27 in turn is held in place by the retainer strips 28 and retainer pins 29. The degree of pivotal movement of the equalizer bar 26 with respect to the slide member 22 is governed by the bevelled lower end of the intermediate, shortened plate 23 of the slide member 22. As a result of this assembly, extension of the hydraulic cylinder I9 moves the slide member 22 downwardly and the center of the equalizer bar 26 is displaced a like distance.

As illustrated in FIGS. 2 and 5, the improved chain equalizer 11 further includes a pair of spaced, vertically extending equalizer frames 30 disposed equidistant from the drill string axis. Each of the frames 30 comprises two parallel, elongate side plates 31 joined together at their upper ends by two transverse bars 32, 33 which are mounted such that a pair of apertures formed therein are in alignment for the reception of a frame pin 34. The rear of each pin 34 connects with a yoke end 35 of the equalizer bar 26, as shown in FIG. 6, and each frame pin 34 is held captive by a set of retainer plates 36. The side plates 31 of each equalizer frame 30 are also connected at their lower ends by a L-shaped crossbrace 37.

As a feature of the invention, the equalizer frames 30 each include an upper guide member 38 that has a vertical guide strip 39 slidably received in an upper guide bracket 40 fixed to the transverse beam 12 (See FIG. 7). Similarly, at the bottom of each equalizer frame 30 there is a lower guide member 41 having a vertical guide strip 42 that slides within a lower guide bracket 43 mounted on the crosstube 13 (See FIG. 9). The equalizer frames 30 are thus vertically guided on the mast 2 to provide a floating" adjustment useful in maintaining proper tensioning of the chains 8.

A pair of upper and lower chain sprockets 44 and 45 is disposed between the side plates 31 of each of the equalizer frames 30 and has peripheral sectors in engagement with the chains 8. The upper sprockets 44 are each rotatably mounted upon a sprocket pin 46 extending through and fastened to the side plates 31. Thus, each sprocket 44 is fixed in position with respect to the equalizer frame 30 in which it is mounted. Each of the lower sprockets 45, on the other hand, is vertically slidable as well as being rotatable with respect to its equalizer frame 30. This sliding mounting is achieved through the use of carrier inserts 47 that will now be described.

With reference to FIGS. 5, 8 and 9, each of the carrier inserts 47 has a base 48 from which extends a pair of spaced, upstanding, flat legs 49 to which are welded at their upper ends a pair of vertical bars 50. As shown in FIG. 9, the bars 50 are oriented in planes ninety degrees from the flat legs 49, and they are in guided, slid ing engagement with the inside surfaces of the side plates 31 of the associated equalizer frame 30. The bars 50 are also guided in their vertical movement by a set of four strips 51 welded to the inner side walls of the side plates 31. The strips 51 and side plates 31 thus define a vertical slideway for the associated carrier insert 47, and to limit the upward movement for the carrier insert 47 a pair of motion limiting pads 52 are positioned above the bars 50.

The vertical bars 50 of an equalizer frame 30 are formed with apertures which receive a bearing pin 53 that rotatably mounts the associated lower sprocket 45. A coil compression spring 54 is disposed about the lower portion of the upstanding legs 49 of each carrier insert 47 and has a lower end working against the base 50 and an upper end working against a circular collar 55 on the underside of the equalizer frame 30. The collar 55 has a rectangular opening, as seen in FIG. 10, through which the upstanding legs 49 may slide.

In assembly, a carrier insert 47 and lower sprocket 45 are introduced into the lower end of each equalizer frame 30 between the side plates 31 with the bore of the lower sprocket 45 and the apertures of the vertical bars 50 aligned with the apertures 56 formed through both of the side plates 31. The bearing pin 53 is then inserted through one of the apertures 56 and into the vertical bars 50 to rotatably mount the lower sprocket 45 as a part of the carrier insert 47. Each carrier insert 47 is then slidably moved toward its uppermost limit defined by the limiting pads 52, and when the chains 8 are adjusted they will suspend the lower sprockets 45 and their carrier inserts 47 at some point below the uppermost position of FIGS. 1, 2 and 5. Each of the compression springs 54 being disposed at the bottom of the equalizer frames 30 tends to bias the lower sprockets 45 downwardly against the chains 8 during times when the hydraulic cylinder 19 is not in actuation.

When the mast I is raised and drilling operations are undertaken the chains 8 are driven to either pull down or hoist the drill string rotating mechanism 4. It is necessary to place the chains 8 under adequate tension, and for this purpose the hydraulic cylinder 19 is constantly pressurized, say at a typical level of 800 psi. This pressure vertically displaces the slide member 22 downward and transmits the force through the equal izer bar 26 directly to the equalizer frames 30. As variable reaction forces occur in the chain drives the equalizer bar will pivot to maintain the tension forces in each chain 8 equal. The forces will also be of such magnitude that the chains 8 will draw the lower sprockets 45 upward relative to the equalizer frames 30, so that the vertical bars 50 bottom out against the motion limiting pads 52. The coil springs do not, then, play a role in tensioning the chains 8 during drilling cycles, either during pull down or hoisting. Tension forces in the chains 8 can be regulated by cylinder pressure, and the forces in the two chains 8 are maintained equal through the action of the equalizer bar 26. When drilling ceases, and the drive sprocket 9 is stopped, then the coil springs 54 act to maintain sufficient chain tension to retain the chains 8 in engagement with their sprockets.

Utilization of the hydraulic cylinder 19 eliminates the need for two spring mounted chain sprockets in each equalizer frame, as in the prior art, and greatly reduces the amount of supplementary manual adjustment required in previous chain tightening arrangements. Due to the floating" vertical movement of the slidably mounted equalizer frames 30, downward tension upon each of the chains 8 may be positively directed, such that a balance of forces is continually maintained.

We claim:

1. In a dual chain equalizer for equalizing the tension in chains of a drill string rotating mechanism of a drilling apparatus having a mast, the combination comprising:

two spaced, vertical equalizer frames slidably mounted on the mast, one of said equalizer frames being positioned on each side of the drill string axis;

each of said equalizer frames having a pair of vertically spaced sprockets rotatably mounted thereon in engagement with the chains of the drill string rotating mechanism, one of said sprockets being slidably disposed and biased downwardly against one of the chains of the drill string rotating mechanism;

an equalizer bar connected between said equalizer frames;

a slide member pivotably attached to the midpoint of said equalizer bar; and

a hydraulic cylinder associated with the mast and having one end connected with and activating said slide member for vertical displacement whereby said equalizer bar shifts said equalizer frames in response to variable chain pressures to keep the chains of the drill string rotating mechanism taut.

2. A dual chain equalizer as in claim 1 having a carrier insert slidably disposed within each of said equalizer frames and connected with each said lower sprocket, each said insert including biasing means mounted to the lower end thereof at the bottom of each said equalizer frame.

3. A dual chain equalizer as in claim 2 wherein each of sid equalizer frames includes guide strips which are slidably engageable with guide brackets affixed to the 

2. A dual chain equalizer as in claim 1 having a carrier insert slidably disposed within each of said equalizer frames and connected with each said lower sprocket, each said insert including biasing means mounted to the lower end thereof at the bottom of each said equalizer frame.
 3. A dual chain equalizer as in claim 2 wherein each of sid equalizer frames includes guide strips which are slidably engageable with guide brackets affixed to the mast. 